If you are trying to make La mian (handpulled noodles) you can subsitue the kansui powder with baking soda since the chemcial compound is similar.

I use 200g of cake$pastry flour2 grams salt1 gram of baking soda

the kneading and dividing takes a lot of practice. I havent succesfully do the wholeroutine yet but I was able to pull some small noodles making some edible noodles. my best advice based on my experience is to keep the dough as even as possible and keep an eye of the center of gravity of your dough . fast gentle tugs works well for me and keep them on the table since its easier to pull them that way.

Kansui in liquid form is available in Chinese markets under the Koon Chun brand. It comes in a clear glass bottle labeled "potassium carbonate & sodium bi-carbonate solution" and the UPC is 0-20717-80230-8.